Saaalaaaaam,
It's a demand
or a curiosity of Mas'Ala.
I don't know about this Mas'Ala either it is Haram or not.
But you Know sister in the old age our Muslim sisters were ride Horses. But i think it could about urgency or necessity if a Sister need to do(with care of her physical appearance of course). I think u can understand what i mean.
Any way i get a link that may help us to understand.
http://islamqa.info/en/152058